The six-hour window for clot removal after stroke might be too short, according to a new study. A report in The New England Journal of Medicine suggests instead that clot removal up to 24 hours later could be effective in reducing disability in certain patients.

The results were from the DAWN trial, an international, multicenter clinical study involving about 200 stroke victims who sought care at a hospital within six to 24 hours after the event. Patients in the study were randomly assigned either to thrombectomy or to standard medical therapy. The difference in results was stark. Although 48.6% of patients undergoing clot removal showed a significant decrease in disability — measured by their independence in activities of daily living 90 days after treatment — only 13.1% of the medication group had similar results. Mortality and other safety endpoints did not differ between the groups, the researchers note.

“These findings could impact countless stroke patients all over the world who often arrive at the hospital after the current six-hour treatment window has closed,” pointed out co-principal investigator Raul Nogueira, MD, professor of neurology, neurosurgery, and radiology at Emory University School of Medicine and director of neuroendovascular service at the Marcus Stroke & Neuroscience Center at Grady Memorial Hospital.

Nogueira suggested that the extent of tissue damage and other clinical factors were more important in determining the utility of thrombectomy than using a rigid time window.

“When the irreversibly damaged brain area affected by the stroke is small, we see that clot removal can make a significant positive difference, even if performed outside the six-hour window,” added co-principal investigator Tudor Jovin, MD, director of the University of Pittsburgh Medical Center Stroke Institute. “However, this does not diminish urgency with which patients must be rushed to the ER in the event of a stroke. The mantra ‘time is brain’ still holds true.”

Starting in September 2014, the study originally planned to enroll 500 patients, but the research was terminated early, in February 2017, after clot removal was shown to be so superior.

The study enrolled patients with occlusion of the intracranial internal carotid artery or proximal middle cerebral artery. All participants had been known to be well six to 24 hours earlier and all had a mismatch between the severity of the clinical deficit and the infarct volume defined by age — younger or older than 80. Results indicate that the mean score on the utility-weighted modified Rankin scale at 90 days was 5.5 in the thrombectomy group vs. 3.4 in the control group.

“Among patients with acute stroke who had last been known to be well 6 to 24 hours earlier and who had a mismatch between clinical deficit and infarct, outcomes for disability at 90 days were better with thrombectomy plus standard care than with standard care alone,” study authors conclude.

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